The present inventive concept relates to semiconductor memories. More particularly, the inventive concept relates to a nonvolatile semiconductor memory device.
Semiconductor memory devices use the semiconducting properties of such materials as silicon (Si), germanium (Ge), gallium arsenide (GaAs), indium phosphide (InP), etc., to store data. Semiconductor memory devices may be classified as volatile or nonvolatile semiconductor memory devices.
A volatile semiconductor memory device loses its stored data when its power supply is interrupted. Examples of volatile semiconductor memory devices are a static RAM (SRAM), a dynamic RAM (DRAM), and a synchronous DRAM (SDRAM). A nonvolatile memory device retains its stored data even when its power supply is interrupted. Examples of nonvolatile semiconductor memory devices are a read only memory (ROM), a programmable ROM (PROM), an electrically programmable ROM (EPROM), an electrically erasable and programmable ROM (EEPROM), a flash memory, a phase change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), and a ferroelectric RAM (FRAM). A flash memory may be classified as a NOR type flash memory or a NAND type flash memory.
As a way to increase the degree to which semiconductor memory devices may be integrated, a semiconductor memory device having a three-dimensional array structure is being studied.